One class of processes for removing materials from microfeature workpieces uses abrasive particles to abrade the workpieces either with or without a liquid solution. For example, mechanical and chemical-mechanical processes (collectively “CMP”) remove material from microfeature workpieces in the production of microelectronic devices and other products. FIG. 1 schematically illustrates a rotary CMP machine 10 with a platen 20, a head 30, and a planarizing pad 40. The CMP machine 10 may also have a conventional subpad 25 between an upper surface 22 of the platen 20 and a lower surface of the planarizing pad 40. A drive assembly 26 rotates the platen 20 (indicated by arrow F) and/or reciprocates the platen 20 back and forth (indicated by arrow G). Since the planarizing pad 40 is attached to the subpad 25, the planarizing pad 40 moves with the platen 20 during planarization.
The head 30 has a lower surface 32 to which a microfeature workpiece 12 may be attached, or the workpiece 12 may be attached to a resilient pad 34 in the head 30. The head 30 may be a weighted, free-floating wafer carrier, or the head 30 may be attached to an actuator assembly 36 (shown schematically) to impart rotational motion to the workpiece 12 (indicated by arrow J) and/or reciprocate the workpiece 12 back and forth (indicated by arrow I).
The planarizing pad 40 and a planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the workpiece 12. The planarizing solution 44 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the microfeature workpiece 12, or the planarizing solution 44 may be a “clean” non-abrasive planarizing solution without abrasive particles. In most CMP applications, abrasive slurries with abrasive particles are used on non-abrasive polishing pads, and clean non-abrasive solutions without abrasive particles are used on fixed-abrasive polishing pads.
To planarize the microfeature workpiece 12 with the CMP machine 10, the head 30 presses the workpiece 12 face-down against the planarizing pad 40. More specifically, the head 30 generally presses the microfeature workpiece 12 against a planarizing surface 42 of the planarizing pad 40 in the presence of the planarizing solution 44, and the platen 20 and/or the head 30 moves to rub the workpiece 12 against the planarizing surface 42.
One challenge of CMP processing is to consistently produce uniformly planar surfaces on a large number of workpieces in a short period of time. Several variables influence the performance of CMP processes, and it is important to control the variables to uniformly remove material from microfeature workpieces. The mechanical and geometric properties of the subpad 25 and the planarizing pad 40 are variables that can affect the uniformity of the planarized surfaces and the polishing rate of the process. For example, grooves or other features on the planarizing pad 40 will affect the distribution of planarizing solution under the workpieces, and the hardness of the planarizing pad 40 will affect the polishing rate and the local conformity of the planarizing surface 42 to the contour of the workpiece 12. Similarly, the hardness and elasticity of the subpad 25 will affect the global compliance of the polishing pad 40 to the workpiece. As such, it is desirable to control the properties of the subpad 25 and the polishing pad 40.
One type of existing subpad, called a filled subpad, has a polymeric matrix and a filler material in the matrix. The filler material can be polymer spheres, or the filler material can be silica particles, alumina particles, other metal oxide particles, or other inorganic particles that fill spaces within the polymeric matrix. The filler materials are generally used to reduce the manufacturing cost. Conventional subpads often have a polymeric matrix without a filler material. Conventional subpads and existing subpads, however, may not perform well for sufficient periods of time.
One drawback of conventional unfilled subpads and existing filled subpads is that their mechanical properties may change over time and lead to a degradation of performance. For example, the polymeric matrix of most subpads will absorb water and other liquids used in the planarizing solutions. The mechanical properties of the subpads will accordingly change depending upon the extent of liquid absorption. This not only degrades the performance of the CMP process and leads to non-uniformities on the planarized surfaces, but it also shortens the pad life and increases the operating costs of CMP equipment.
Another drawback of subpads with filler materials is that the subpads may not have the optimal mechanical properties. More specifically, many desirable filler materials may not be suitably compatible with the polymeric matrix materials. The lack of compatibility between filler materials and polymeric materials can limit the mechanical properties of the subpads. As a result, subpads with filler materials may not perform at optimal levels. Therefore, it would be desirable to enhance the performance of subpads with filler materials.